1. Field of the Invention
The present invention relates to a memory element, and more particularly to a memory element which is suitable for driving a pixel in an active matrix type liquid crystal display device. In addition, the present invention relates to an active matrix type liquid crystal display device in which such memory elements are formed in each of pixels.
2. Description of the Related Art
An active matrix type liquid crystal display device includes gate lines wired in rows, data lines wired in columns, and pixels disposed in portions in which both the gate lines and the data lines intersect with each other, respectively. An electro-optic element typified by a liquid crystal cell, and an active element such as a thin film transistor for driving the electro-optic element are formed in each of the pixels. A gate of the thin film transistor is connected to corresponding one of the gate lines, a source thereof is connected to corresponding one of the data lines, and a drain thereof is connected to corresponding one of the electro-optic elements. In the active matrix type liquid crystal display device, the gate lines are scanned in a line-sequential manner, and a video signal (data) is supplied to the data lines wired in columns in correspondence to the scanning operation, thereby displaying an image corresponding to the video signal in a pixel array.
In the active matrix type liquid crystal display device, the gate lines are scanned in the line-sequential manner every one field, and the video signal is supplied to the data lines in correspondence to the scanning operation. In the case of display of a moving image, since a picture is switched over to another one every one field, it is necessary for the data lines to repeat charge and discharge of the video signal every one field. When a liquid crystal display panel of the active matrix type liquid crystal display device is driven, the most part of power consumption is consumed for the charge and discharge of the data lines.
The lowering of a rewrite frequency (field frequency) of an image is effective in suppression of the power consumption consumed for the charge and discharge of the data lines. However, it is well known that when the field frequency is lowered to 30 to 60 Hz or less, a flicker occurs in a screen, thereby deteriorating the display characteristics. In order to cope with this problem, heretofore, a system for giving each of the pixels a memory function, thereby reducing the number of times of the charge and discharge is proposed as the means for saving the power consumption without lowering the field frequency. This technique, for example, is described in Japanese Patent Laid-Open No. Hei 11-52416, a non-patent literary document 1 of M. Senda et al.: “Ultra low power polysilicon AMLCD with full integration” SID2002, p. 790, a non-patent literary document 2 of S. Q. Liu, N. J. Wu, and A. Ignatieva: “Space Vacuum Epitaxy Center and Texas Center for Superconductivity,” University of Houston, Houston, Tex. 77204-5507, “Electric-pulse-induced reversible resistance change effect in magnetoresistive films,” APPLIED PHYSICS LETTERS, VOLUME 76, NUMBER 19, 8 May 2000, and a non-patent literary document 3 of Akihito SAWA, Takeshi FUJII, Masashi KAWASAKI and Yoshinori TOKURA: “Colossal Electro-Resistance Memory Effect at Metal/La2CuO4 Interfaces,” Japanese Journal of Applied Physics, Vol. 44, No. 40, 2005, pp. L1241 to L1243.